1. Field of the Invention
The present invention relates generally to the field of semiconductor manufacturing and more particularly to methods for removing perfluorinated compounds from waste gases produced by semiconductor manufacturing processes.
2. Description of the Prior Art
Perfluorinated compounds (PFCs) comprise a class of molecules characterized by one or more carbon atoms with one or more fluorine atoms that may additionally include atoms of hydrogen and/or oxygen. PFCs are typically gases under ordinary conditions. Exemplary PFC gases include CF4, C2F5H, C2F2H4, CF3H, C2F6, C3F8, C4F8, and C4F8O. PFCs have been found to be damaging to the environment and are recognized as a contributing factor to greenhouse warming. Unfortunately, many manufacturing processes, and particularly semiconductor manufacturing processes, rely on various PFCs and adequate replacements have not been identified, so preventing these PFCs from entering the atmosphere has become a manufacturing imperative.
Abating PFCs, however, is very difficult in that they do not readily absorb, burn, or adsorb. Nevertheless, one existing method burns PFCs with a very high temperature methane flame. This method has several drawbacks, however. First, achieving the required temperature consumes a large flow of methane and pure oxygen. This is both expensive and produces a large quantity of carbon dioxide, another greenhouse gas. In addition, this method is not very effective for removing certain PFCs such as carbon tetrafluoride, commonly used in semiconductor manufacturing.
Another method for PFC abatement routes the PFCs through a plasma device. One problem is that maintaining a plasma requires sophisticated technicians. Another is that the devices are prone to fail, especially where the flow vacillates or where there is heavy fouling in the discharge stream.
A third method for abating PFCs employs a catalyst to catalyze a decomposition reaction. There are a number of challenges in developing a robust and sustainable catalytic abatement system, however. One challenge is that the catalyst must be effective in promoting the decomposition of PFCs that are very stable and typically not very reactive. Second, the system must protect the catalyst from poisoning and fouling from other compounds in the stream such as acids, halogen gases, and particulates. Finally, the catalyst, and the substrate that supports the catalyst, must be capable of withstanding very high temperatures required to activate the decomposition reaction and must also be resistant to the acid gases formed by the PFC decomposition.
Consequently, there is a need for methods that effectively and economically treat the discharges from semiconductor manufacturing lines to prevent the release of PFCs and that comply with international treaties on greenhouse gases.